A thermal printer of a thermal transfer system is widely used as a printer such as a barcode printer or a label printer, which transfers ink coated on an ink ribbon with a thermal head by melting the ink by heat. As a result, in a printer using the ink ribbon, an unused ink ribbon fed from a ribbon holding shaft is wound by a ribbon winding shaft through a printing position where a thermal head and a platen face each other to perform thermal transfer. On the other hand, a print medium is conveyed by a conveyance section, but it is desired that the ink ribbon and the print medium are conveyed synchronously in the same direction and at the same speed at the above-mentioned printing position, thereby preventing rubbing and dirt and further improving printing quality.
Conventionally, there is a method of detecting a rotation speed of each rotation shaft using an encoder that detects transmitted light by providing a slit in each of the ribbon winding shaft and the ribbon holding shaft or a gear attached to each rotation shaft, and further calculating a ribbon diameter (a winding diameter of the ink ribbon) for each shaft. As a result, the printer applies an input voltage corresponding to the ribbon diameter at that time to a motor for driving each rotation shaft and controls a torque of each rotation shaft, thereby controlling a conveyance speed and tension of the ribbon and further improving the printing quality.
However, at the time of turning on a power supply or at a time point before the start of the conveyance of the ink ribbon immediately after the ink ribbon is replaced, since the rotation shafts do not rotate, the ribbon diameter cannot be calculated. Therefore, conventionally, at the start of conveyance of the ink ribbon, an intermediate value between the ribbon diameter at the start of use of the ink ribbon and the ribbon diameter at the time when there is no ink ribbon is used to set an initial input voltage applied to the motor which corresponds to the ribbon diameter.
As a result, since the initial input voltage is set using the ribbon diameter different from the actual ribbon diameter, there is a case in which the motor input voltage at the start of the winding operation of the ink ribbon does not match the actual ribbon diameter. There is also a problem that wrinkles occur in the ink ribbon and phenomena such as smudge generated as the ribbon and the paper are not synchronized in speed and are rubbed and stained occur. Therefore, conventionally, a technology capable of more appropriately setting the motor input voltage at the start of the winding operation of the ink ribbon is desired.